U.S. patent number 4,707,655 [Application Number 06/743,589] was granted by the patent office on 1987-11-17 for contact for multicontact probe assembly.
This patent grant is currently assigned to Feinmetall GmbH. Invention is credited to Gustave Kruger.
United States Patent |
4,707,655 |
Kruger |
November 17, 1987 |
Contact for multicontact probe assembly
Abstract
A contact for a multicontact probe assembly for testing at least
partially conductive elements has a conductive contact rod
extending along a axis and having a rear end and a forwardly
directed and pointed front test end of construction suitable for
using alone as a test point. A respective conductive cap engageable
axially snugly over the pointed front end of the rod can be
releasably secured on the pointed front end for use of the same rod
to test, for example, a bushing or a bore connection. Thus a single
contact can serve several functions, making the probe assembly
having it much more versatile than prior-art systems. Only some of
the contact rods of a probe assembly, those destined to engage
large-diameter bores or bushings, need be equipped with the heads,
and the small pointed tips of the remaining rods of the assembly
can engage and contact the strips or smaller holes or bushings
directly.
Inventors: |
Kruger; Gustave (Herrenberg,
DE) |
Assignee: |
Feinmetall GmbH (Herrenberg,
DE)
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Family
ID: |
6238138 |
Appl.
No.: |
06/743,589 |
Filed: |
June 11, 1985 |
Foreign Application Priority Data
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Jun 12, 1984 [DE] |
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3421720 |
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Current U.S.
Class: |
324/755.01;
324/763.01; 439/482 |
Current CPC
Class: |
H01R
13/2421 (20130101); G01R 1/067 (20130101) |
Current International
Class: |
G01R
1/067 (20060101); H01R 13/24 (20060101); H01R
13/22 (20060101); G01R 001/06 () |
Field of
Search: |
;324/158P,158F,73PC,72.5,149
;339/95R,96,97T,15B,18TP,255R,252R,17M,17LM |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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3340184 |
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May 1985 |
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DE |
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60-49270 |
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Mar 1985 |
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JP |
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723703 |
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Apr 1980 |
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SU |
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Primary Examiner: Eisenzopf; Reinhard J.
Assistant Examiner: Baker; Stephen M.
Attorney, Agent or Firm: Teltscher; Erwin S.
Claims
I claim:
1. A contact for a multicontact probe assembly for testing at least
partially conductive elements, the contact comprising
a conductive contact rod extending along an axis, and having a rear
end, and a front end,
a conductive cap engageable axially snugly over the front end of
the rod, said front end being pointed so as to serve as a test end
for testing said conductive elements upon said cap being removed
from said front end of said rod, and
securing means for releasably securing said cap on said front end,
whereby at least two differently formed test contacts are
obtainable on said probe assembly by selectable use and non-use of
said cap.
2. The contact defined in claim 1, wherein the cap is formed at the
axis with an axially throughgoing bore, the front end of said
contact rod fitting into said bore so that said cap is axially
placeable on said front end.
3. The contact defined in claim 1, wherein said securing means is a
collar formed on said cap and provided with a plurality of
rearwardly open slots so as to elastically grip said rod in back of
its front end.
4. The contact defined in claim 1, wherein said conductive contact
rod has a predetermined width in a region of said front end, and a
width substantially equal with said predetermined width in another
region behind the front end region.
5. The contact defined in claim 1, wherein said rod has a
predetermined diameter, and said cap has a substantially greater
diameter than said predetermined rod diameter.
6. The contact defined in claim 1, wherein the cap is formed at the
axis with an axially throughgoing bore, the rod front end fitting
into said bore and projecting axially from the cap beyond said
bore.
7. The contact defined in claim 1, wherein the cap has a front
surface lying on a frustocone centered on the axis.
8. The contact defined in claim 7, wherein the cap is formed with
axially forwardly projecting and radially extending teeth having
edged extending generally radially from the vicinity of the cap
center outwardly, and lying on the frustocone, each edge having a
substantially triangular cross-section with an apex thereof
pointing outwardly.
9. The contact defined in claim 1, further comprising support means
engaged axially behind the contact rod for resilient axial
displacement thereof.
10. The contact defined in claim 9, wherein said support means
includes a cylinder and a spring braced between a closed end of
said cylinder and a rear end of said contact rod.
11. The contact defined in claim 1, wherein said contact rod is
rigid.
12. The contact defined in claim 1, wherein said conductive cap has
a front surface adapted for making contact with test points of said
conductive elements.
13. The contact defined in claim 12, wherein said cap front surface
is substantially conical.
14. The contact defined in claim 1 wherein the front end of the rod
engaged with spacing in the cap.
15. A contact for a multicontact probe assembly for testing at
least partially conductive elements, the contact comprising
a conductive contact rod extending along an axis, and having a rear
end, and a front end,
a conductive cap engageable axially snugly over the front end of
the rod, said front end being pointed so as to serve as a test end
for testing said conductive elements upon said cap being removed
from said front end of said rod,
securing means for releasably securing said cap on said front
end,
resilient means engaged axially behind said contact for resilient
axial displacement thereof, and
freedom-of-movement means interconnected between said resilient
means and said contact rod for permitting said contact rod limited
lateral deflection
whereby at least two differently formed test contacts are
obtainable on said probe assembly by selectable use and non-use of
said cap.
16. A contact head for use in conjunction with a multicontact probe
assembly for testing at least partially conductive elements, the
contact head comprising
a conductive cap adapted to releasably engage a front end of a
contact rod of said multicontact probe along an axial direction
thereof,
said conductive cap having a front surface adapted to be make
contact wtih test points of said conductive elements, and being
also engageable axially snugly over the front end of the rod,
said front end being pointed so as to serve as a test end for
testing said conductive elements upon said cap being removed from
said front end of said rod, and
securing means for releasably securing said cap on said front
end,
whereby at least two differently formed test contacts are
obtainable on said probe assembly by selectable use and non-use of
said cap.
Description
FIELD OF THE INVENTION
The present invention relates to a device used typically to test
printed-circuit boards and the like and having a multicontact probe
assembly. More particularly this invention concerns the contact
that is used in such a probe assembly.
BACKGROUND OF THE INVENTION
A printed-circuit board is a dielectric plate carrying on one or
both faces a network of lines of a conductive material such as
copper that are either printed on the plate or created by etching
out the copper between the lines on a completely copper-plated
plate. The board is drilled at the conductive lines to create holes
that allow the leads of circuit elements to be soldered in place
and that allow if necessary connection to be made from a line on
one face of the board to a line on the opposite face. Before
circuit elements are soldered to the board it is necessary to test
it, both to ascertain that each of the lines is electrically
continuous, and to verify that there are no unwanted connections
between lines that are supposed to be electrically independent. Any
error whatsoever of continuity or discontinuity makes the board
usable, a reject.
The testing apparatus has a probe assembly with a multiplicity of
finger-like contacts whose tips are simultaeously brought into
contact with the various lines. The contacts are arrayed such that
one contact engages each end of each conductive line or the end of
any extension thereof. Such an arrangement is described in jointly
filed and copending patent application Ser. No. 743,671 now U.S.
Pat. No. 4,686,465.
To accommodate different sizes of boards the support board of the
probe assembly is provided with a multiplicity of densely spaced
depressible supports. A tight grid of such supports is provided,
with the supports independently connected to an electronic test and
analyzing device, and the grid is at least as large as the largest
board to be tested. Thus when the board to be tested and the array
of supports are juxtaposed, there will be at least one support
generally aligned with the end of every line or segment thereof as
well as with any bores in the board. The contacts are rods
supported on those supports which lie generally in the right
position relative to the locations to be contacted. Only those
contacts needed for a specific test are mounted on supports, and a
mask is provided to orient the forward ends of the contact rods
appropriately for the specific board being tested. The supports
allow the contact rods to be depressed back into the probe assembly
so that when the board is pressed back or the assembly is pressed
up against the board the contacts will all bear with a certain
standard pressure against the points being tested, thereby making
the resistance at the interface between the front end of the
contact and the line being tested uniform for all the contacts.
For best contact with a standard printed-circuit conductor line it
is standard to use contact rods whose forward contact ends are
somewhat pointed. When they are to be used to test a grommet,
socket, or similar bushing fitted in the board it is standard as
described in U.S. Pat. No. 3,676,776 to form the contact ends of
the rods as balls so that they will naturally fit and center
themselves within the invariably circular holes and collars on the
boards. This patent also describes an arrangement wherein the
contact rod is cylindrical with a squared-off front end which
carries a part-spherical removable tip. It is further possible to
form the tip with a rearwardly projecting end pin that can fit in
the front end of the rod. Such an arrangement allows the tips to be
changed for different applications, nonetheless it requires that a
complete set of tips be maintained on the contacts at all times,
and the necessary construction is often expensive or requires
relatively thick contact rods to be used.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide an
improved contact for a multicontact probe assembly.
Another object of the invention is to provide a conductive cap
engageable with a front end of a contact rod and adapted to contact
differently formed test points of a circuit board, without the
contact rods themselves having to be changed or replaced.
SUMMARY OF THE INVENTION
This object is attained in a contact for a multicontact probe
assembly for testing at least partially conductive elements, and
wherein the contact includes a conductive contact rod extending
along an axis and has a rear end and a front end, by providing a
conductive cap axially engageable over the front end of the rod,
and securing means for releasably securing the cap on the front
end.
As a result of the replaceable cap the contact rods of the contact
or contact element may be matched to differently formed test points
on the conductive elements, simply by fitting over the contact rods
of the contact or contact element caps matched to the respective
test points. It will of course be understood that where it is not
necessary to fit a contact rod with a cap, as the assembly of
contact rods is already matched to the test points of the circuit
board, it is preferable not to use the cap. The cap will only be
used when its use is necessary in relation to the test points to be
tested.
As a result of the present invention it is therefore no longer
necessary to replace the contact rods, or the entire contacts, if
the geometry of the tip of the contact rods must be changed in
order to match it to the test points of the circuit board.
The invention also covers a contact head itself, wherein the
contact head includes the cap employed in the inventive contact for
a multicontact probe assembly, as the contact head may be
manufactured and sold separately, independently of the inventive
contact.
The securing means releasably securing the cap to the front end of
the contact rod may be implemented in various ways. It is
particularly simple and advantageous if the cap is firmly seated on
the contact rod, being held thereto, for example, by friction, but
wherein it can nevertheless be easily removed from the seat, and
again fitted thereonto easily, such as providing a snap fit over a
bump, a sliding fit or the like.
The cap is secured to the contact rod in a particularly simple and
reliable manner, which also permits a high degree of tolerance, if
the securing means is a collar formed on the cap and provided with
a plurality of rearwardly open slots so as to elastically grip the
rod in back of its front end.
Other securing means are also conceivable. Thus in many cases it
may be advangtageous to provide the cap with an inner thread, which
in turn may be threaded onto an outer thread on the contact rod. It
is also possible to employ a bayonet coupling to secure the cap to
the contact rod. But other possibilities exist also. Thus in many
cases it may be advantageous to provide the aforedescribed snap fit
over a bump. In a variant of this inventive thought, the
aforedescribed collar formed with the aforedescribed rearwardly
open slots is made so that the resultant fingers are bent somewhat
inwardly and engage an annular groove formed in the contact rod
when the cap is fitted theronto.
According to another feature of this invention the cap has a front
surface lying on a frustocone, that is the outer surface of a
truncated cone, centered on the axis. The front face can be
smoothly conical or frustoconical, or the front face of the cap can
be formed with axially forwardly projecting and radially extending
edges lying on the frustocone. This provides good scraping action,
which is particularly useful when engaging a bushing or the like
which might have oxidized.
DESCRIPTION OF THE DRAWING
FIG. 1 is an axial section through a contact assembly of a
multicontact probe according to the invention;
FIG. 2 is a large-scale sectional view corresponding to a detail of
FIG. 1 illustrating another contact cap according to the
invention;
FIG. 3 is a view like FIG. 2 through yet another cap in accordance
with this invention;
FIG. 4 is a right-hand end view of the cap of FIG. 3; and
FIG. 5 is another section like FIG. 1 illustrating another contact
assembly according to the invention.
SPECIFIC DESCRIPTION
FIG. 1 shows a contact assembly 12 for a printed-circuit board 19
formed with a hole lined with a bushing 20 having a cylindrical
internal collar or leg 21 snugly fitted in the hole and a planar
outer flange 22 lying on the face of the board 19 around the hole.
The probe assembly has a dielectric base plate 10 provided with an
array of supports for respective contacts 14, which are in a dense
grid array and may number in the thousands. A test device can be
connected as described in the above-cited copending application to
the contacts 14 for measuring current flow between them, as they
are maintained electrically independent by the insulating plate
10.
Each contact 14 is a solid rod 27 made of a rigid and conductive
metal such as steel, brass, or bronze and has a front end formed
with a conically forwardly pointed tip 24 centered on the axis C.
Thus the widest part of the rod 27 is the rear end 25, the front
end either being cylindrical or conical.
Each of the supports is received in a respective bore formed in the
plate 10 and is basically formed of a cylindrical and conductive
guide sleeve 11 having a closed rear end 113 to which a respective
wire 23 is soldered and a spring 15 braced between the closed floor
13 of the sleeve 11 and the plunger-like rear end 25 of the solid
rod 27 forming the rest of the contact 14. The front end of the
sleeve 11 is bent in around the front edge 16 of the enlarged rear
end 25 of the contact 14, to confine same so that it cannot be
pushed forwardly therefrom along the axis C of the sleeve 11 but
can be depressed axially back in the direction A in the sleeve 11
while compressing the spring 15. The rear end 25 of the contact 14
is in excellent electrical contact with the sleeve 11, both by
engagement with the inner faces of the sides thereof and via the
spring 15.
According to this invention the front end 24 of the contact 14
carries a conductive contact cap 17 that has, relative to the axis
C, a massive front head 30 forming a forwardly directed, centered,
and backwardly flaring frustoconical surface 31, and a rearwardly
directed mounting collar 32 formed with a rearwardly open
cylindrical bore 32' having a forwardly tapering and conical front
end 32" and fittin snugly around the rod 27 behind its tip 24. The
metal of the cap 17 is slightly elastic and the collar 32 is formed
with three angularly equispaced, axially rearwardly open and
radially throughgoing slots 33 that allow the collar 32 to engage
elastically and snugly on the front end of the rod 27.
In use the board 19 to be tested is pressed back in direction B
against the probe assembly having a multiplicity of appropriately
arrayed contact assemblies 12. As the bushing 20 engages the cap 17
the contact 14 will be pushed back. Thus the contact 14 will bear
forward on the bushing 20 and backward on the respective sleeve 11
with substantially the same force. The surface 31 is sufficiently
pointed that it will naturally center in the bushing 20 and is of
sufficiently great outer diameter that it cannot, like the rod part
27, engage through and past the bushing 20 without touching it.
In addition according to this invention it would be possible to
eliminate the cap 17 to allow the respective tip 24 to be used
directly to engage, for instance, a portion of a conductive copper
strip on a printed-circuit board, in the manner described in my
above-cited copending patent application.
In the arrangement of FIG. 2 the cap 17a is formed with a bore
32a', 32a" whose rear portion 32a', just like in FIG. 1, is
cylindrical, slotted, and snugly engages the cylindrical body of
the rod 27, but whose front bore portion 32a" is frustoconically
complementary to the tip 24 and axially throughgoing so that this
tip 24 projects axially less than 1mm forward through the cap 17a.
Such an arrangement can serve double duty both as a bushing tester
and a conductor-strip tester.
In the arrangement of FIGS. 3 and 4 the cap 17b is internally
formed with a bore 32b', 32b" identical to that of FIG. 2. The
front face of the cap 17b, however, is formed with six radially
extending, axially centered, and identical teeth 35 having flanks
34 and defining angled straight edges 36 lying on a frustoconical
surface 31b identical to the surface 31 of FIGS. 1 and 2. This cap
17b is self-centering like the caps 17a and 17, and will bear in
line contact via all the individual edges 36 on the bushing 20 for
excellent self-cleaning action as described in the above-cited
copending application. Thus any oxide coat on the bushing 20 being
tested will be scraped off at the contact zones.
FIG. 5 shows how a contact 14c is formed of a rod 27c having a rear
ball end 40 and of a plunger 37 having a front socket end 39 and a
rear end 38 functionally identical to the part 25 of FIG. 1. The
fit of the ball end 40 in the complementarily shaped socket end 39
allows the axis of the rod part 27c to be out of line with the
center axis of the spool plunger 37, as also described in detail in
the copending application. Thus the rod part 27c can fit through a
hole 42 in a mask 41 for engagement with a bushing or conductive
strip not in perfect axial line with the support sleeve 11.
APPLICATIONS OF THE DIFFERENT EMBODIMENTS
With the system of this invention, therefore, the contact rod can
work with or without a cap. When used without a cap, it is
perfectly suited for testing unbored portions of printedcircuit
boards.
However, when a region on a circuit board without a cap 17 secured
to the contact 14 cannot make good or adequate electrical contact
with a test point on the circuit board the cap 17 is then fitted
onto the contact 14. This applies, for example, to the embodiment
of FIG. 1, as the bore 21 of the bushing 22 of the circuit board
19, which is to be tested by the contact element 12, is too large
for the plane contact 14 without a cap.
In the embodiment of FIG. 2 the pointed tip 24 projects beyond the
front surface 31 of the cap 17a; this projection may, for example
be a length of only a fraction of a millimeter. Due to this
projection the contact 14 is not changed in length by the cap being
fitted thereonto. This is particularly advantageous, as the probe
assembly may include a multiplicity of other such contacts 14
without a cap, and still other contacts 14 with caps. It is
avantageous if all contacts 14 have the same length, irrespective
whether they are provided with a cap or not.
The embodiment of FIGS. 3 and 4 is particularly suitable for
applications, such as shown in FIG. 1, where the cap serves to
contact metallic rims of bores in the circuit board, into which the
point 24 projecting from the contact 14 may penetrate, without
making electrical contact with the test region itself; this
electrical contact is performed only by the cap. The apices 36 of
the teeth may, in fact, also be implemented as longitudinal
surfaces of a very small width, which perform, however, a
sufficient scraping action to penetrate any oxidation layers on the
test regions.
The embodiment of FIG. 5 is particularly suitable for those
applications, as outlined in the aforesaid copending patent
application, where the openings in the mask, as referenced in the
aforesaid copendig patent application, are not completely aligned
with the test points on the circuit board. The degree of lateral
omvement is set by the limits of the pivoting action of the ball
joint consisting of elements 40 and 39.
While the invention has been illustrated in preferred embodiments,
it is not to be limited to the structures shown, since many
variations thereof will be evident to one skilled in the art and
are intended to be encompassed in the present invention as set
forth in the following claims.
* * * * *